Waterborne polyurethane dispersions have been used in many applications because of their zero/low-VOC and drying characteristics. This technology is based on the preparation of high molecular weight particles of polyurethane polymers in water. As the water leaves the applied coating, these particles coalesce, forming a non-cross-linked finished film. The performance of these coatings is generally-inferior to one- or two-component cross-linked films in terms of chemical resistance and mechanical durability, particularly in so-called “soft-touch” coatings. One variation of this technology makes use of the preparation of these waterborne polyurethane dispersions with an excess of hydroxyl groups for use in conventionally curing one- and two-component crosslinked coatings. These two types of waterborne polyurethane dispersions can be combined together with water reducible polyisocyanates to form two-component waterborne soft touch coatings with improved general performance. These coatings typically require forty-five minute cure cycles before any properties can be developed (usually fifteen minutes at ambient temperature and thirty minutes at elevated temperatures.
Typical of the prior art, waterborne dispersions used for soft touch coatings are described in U.S. Pat. Nos. 6,211,286, 6,254,937, and 6,414,079, and in U.S. Application Publications 2002/0137828 and 2002/0147253.
Radiation curable polyurethane coating compositions are also known (see, e.g., U.S. Pat. Nos. 5,135,963, 6,011,078, 6,207,744, 6,335,397, 6,436,540, and 6,538,046, and German Published Application 40 31 732.
Finally, radiation curable, waterborne polyurethane dispersions based at least in part on unsaturated polyesters and/or polyester acrylates are also known (see, e.g., U.S. Pat. Nos. 5,684,081 and 6,521,702).
In spite of all the known technology, the art has not yet described a composition for use in soft touch coatings that cure relatively rapidly and form films having a soft feel, good chemical resistance, hydrolytic stability and toughness (i.e., flexibility and mechanically durable).